Global system for mobile communications (GSM) Release 7 (R7) introduces several features to improve throughput in the uplink (UL) and downlink (DL), as well as to reduce latency of transmissions.
Among these, GSM R7 will introduce enhanced general packet radio services-2 (EGPRS-2) to improve throughput for the DL and the UL. EGPRS-2 throughput improvements in the DL are known as the REDHOT feature, and improvements for the UL are known as the HUGE feature. EGPRS-2 DL and REDHOT are synonym. Similarly, EGPRS-2 UL and HUGE are synonym.
In addition to legacy enhanced general packet radio service (EGPRS) modulation and coding schemes (MCS) based on Gaussian minimum shift keying (GMSK) (MCS-1 through MCS-4) and 8 phase-shift keying (8PSK) modulations (MCS-5 through MCS-9), EGPRS-2 DL will use quadrature PSK (QPSK), 16 quadrature amplitude modulation (16QAM) and 32QAM modulations. Another technique for improved throughput is the use of Turbo coding (as opposed to convolutional coding with EGPRS). Furthermore, operation at higher symbol rate (1.2× symbol rate of legacy EGPRS) with EGPRS-2B DL (or, REDHOT-B) and EGPRS-2B UL (or, HUGE-B) is another improvement.
Latency Reduction (LATRED) is another feature provided by GSM/EDGE radio access network (GERAN) Release 7 (and beyond) to reduce transmission delays, increase data throughput, and to provide better quality-of-service (QoS). The LATRED feature comprises two techniques. The first LATRED technique is reduced transmission time interval (RTTI) mode of operation. The second LATRED technique is fast acknowledgement/non-acknowledgement (ACK/NACK) reporting (FANR) mode of operation.
Both the RTTI feature and the FANR feature can either work separately, or in conjunction with each other. Furthermore, both the RTTI feature and the FANR feature can be used in conjunction with the EGPRS modulation-and-coding schemes MCS-1 to MCS-9 (except for MCS-4 and MCS-9 where FANR mode of operation is not possible), or with the novel Release 7 and beyond EGPRS-2 modulation-and-coding schemes DAS-5 to DAS-12, DBS-5 to DBS-12, UAS-7 to UAS-11 and UBS-5 to UBS-12. Both the RTTI and the FANR modes of operation are also possible with other existing Release 7 GERAN evolution features, and other features beyond for (E)GPRS packet transmission, or methods based thereof, such as for example the Downlink Dual-Carrier (DLDC) feature or Downlink Advanced Receiver Performance (DARP) operation.
In the pre-Release 7 GSM/GPRS/EGPRS modes of operation, an ACK/NACK report is typically sent in explicit radio link control (RLC)/medium access control (MAC) protocol messages, also referred to as RLC/MAC control blocks. Examples for such explicit RLC/MAC protocol messages include packet downlink ACK/NACK or packet uplink ACK/NACK messages. The RLC/MAC control block is addressed to a certain radio resource, called a temporary block flow (TBF).
A TBF is a temporal connection between a mobile station and a network to support a uni-directional transfer of data. If supported by the mobile station and the network, more than one (1) TBF can be allocated to a mobile station. A TBF is temporary and maintained only for the duration of the data transfer. Each TBF is assigned a temporary flow identity (TFI) by the network. The TFI is unique among concurrent TBFs in each direction and is used instead of mobile station identity in the RLC/MAC layer. For example, in GPRS and EGPRS modes of operation, the same TFI is included in every RLC/MAC header belonging to a particular TBF in order to allow the intended receiver, (i.e., the wireless transmit/receive unit (WTRU) or network), to determine the addressee of a received radio block.
In order to reduce transmission latencies associated with the use of an entire RLC/MAC control block, another mode of ACK/NACK operation in GSM/(E)GPRS Release 7 has been incorporated, referred to as FANR mode of operation. The ACK/NACK report for a certain TBF is “piggybacked” onto an RLC/MAC data block by puncturing a number of bits from the channel-coded data portion of the radio block at no loss of data. This new field which is inserted, when needed, into the RLC/MAC data block and which carries the ACK/NACK report as part of the radio block is referred to as a piggybacked ACK/NACK (PAN) field. The insertion of PAN is possible, and can be configured separately, both for the DL and UL directions. The PAN field, when sent to a WTRU in the DL, carries ACKs or NACKs for data units or protocol data units (PDUs) previously sent by the WTRU in the UL direction, and vice versa. The presence or absence of the PAN field in a radio block is indicated by the RLC/MAC header, either by a bit or bit field setting, or by setting other code points depending on the RLC/MAC header type accordingly, and therefore depends on the EGPRS/EGPRS-2 modulation and coding scheme chosen for the transmission of the radio block. In the DL direction, the PAN field of an RLC/MAC data block may possibly be addressed to a WTRU that is not the intended receiver of the data units (or PDUs) in the radio block. Alternatively, the PAN field and the data units (or PDUs) of the radio block may be intended for the same WTRU. Both for DL and UL directions, the TBF to which the PAN field refers may possibly be different from the TBF corresponding to the data units (or PDUs) of the radio block, even if the receiver is the same physical unit (WTRU, or network).
The actual bit field(s) carrying the ACKs or NACKs in the PAN field may be encoded according to either one of two (2) different procedures: a starting sequence number (SSN)-based approach or a time-based (TB)-approach. For both SSN-based and TB FANR operation, the PAN field is in principle the same, but the encoding approach differs.
When the SSN-based ACK/NACK mode is used, the PAN field includes an SSN and a reported bitmap, which relates to a series of RLC/MAC data blocks starting from the SSN. The PAN field contains parameters that can point out what block sequence number (BSN) the bitmap corresponds to. A BSN is included in every RLC data block.
For the TB FANR, the PAN field bits simply comprise a bitmap where pairs of bits refer to the decoding status of one or two RLC data block(s) on a given packet data channel (PDCH) in a given preceding transmission time interval (TTI). The TB ACK/NACK mode is particularly suitable to real time services such as voice over IP (VoIP). When the time-based ACK/NACK mode is used, instead of referencing the ACK/NACK report to SSNs, the ACK/NACK report refers to previously received RLC/MAC data blocks sent and the RLC/MAC data PDU(s) contained therein by one or possibly more WTRU(s) in the UL as given by a known or induced timing relationship. The TB-PAN field includes a bitmap providing feedback information relative to the reception of previously received UL RLC/MAC blocks at the network side. As a function of the size of the bitmap in the PAN field, a certain number of previously received RLC/MAC blocks can be acknowledged. When received in the DL, a TB-PAN field can carry information pertaining to more than one WTRU. Because any WTRU can keep track of when it sent RLC/MAC blocks in the UL, it can unambiguously associate ACK/NACK status in the PAN bitmap with its own transmissions (and ignore those of other WTRUs), because the timing relationship is known and fixed.
The SSN-based FANR method is used to convey ACK/NACKs for the downlink TBFs. However, for the uplink TBFs, either the SSN-based or the TB FANR method may be used. The base station subsystem (BSS) configures the FANR ACK/NACK mode to acknowledge the uplink transmissions when FANR is activated. When the TB-FANR mode is configured, all uplink TBFs in use by the WTRU must operate in the time-based ACK/NACK mode.
In the Release 7 GSM/GPRS/EGPRS modes of operation in conjunction with FANR mode of operation, the pairs of bits in the bitmap are used to refer to one (1) or two (2) RLC data block(s), or PDUs. In the following, we refer to the data units contained in an RLC/MAC data block as RLC data blocks, even though PDUs can be used as a synonym. Four different code points (using two bits) are currently defined in the current third generation partnership project (3GPP) specification (TS 44.060 v.7.10.9 2007-9-25) as shown in Table 1.
TABLE 1BitstringMeaning0 0failed header decodingheader correctly received but failed decoding of the payload ofthe RLC data block (or RLC data blocks, in case of MCS-7/MCS-8/MCS-9)0 1header correctly received, failed decoding of the first RLC datablock, correct decoding of the second RLC data block1 0header correctly received, correct decoding of the first RLC datablock, failed decoding of the second RLC data block1 1correct decoding of the payload of the RLC data block, or correctdecoding of both the first and second RLC data blocks
In all four combinations given by prior art, the maximum number of RLC data blocks, or PDUs, that can be acknowledged is two (2). This is perfectly appropriate for FANR operation in conjunction with legacy enhanced general packet radio services (EGPRS), which at most can have two (2) RLC data blocks per TTI. In EGPRS, an RLC/MAC block using modulation and coding scheme (MCS)-1 to MCS-6 includes one RLC data block, and an RLC/MAC block using MCS-7 to MCS-9 includes two RLC data blocks, as shown in Table 2. FIG. 1 shows an RLC/MAC block for EGPRS data transfer with FANR activated. The RLC/MAC block comprises a combined RLC/MAC header, one or two RLC data blocks, and an optional PAN field.
TABLE 2Channel CodingEGPRS RLC data unit size (N2)Scheme(octets)MCS-122MCS-228MCS-337MCS-444MCS-556MCS-674MCS-72 × 56MCS-82 × 68MCS-92 × 74
However, the current baseline mode of operation with time-based FANR and its pair-wise bitmap definition of the PAN field does not allow for operation in conjunction with the EGPRS-2 UL (or, HUGE) features in Release 7 (R7). FIG. 2 shows an RLC/MAC block for EGPRS-2 data transfer. The RLC/MAC data block comprises a combined RLC/MAC header, one (1) up to four (4) RLC data blocks, and an optional PAN field which is included in case FANR is activated. Similarly, EGPRS-2 DL (or REDHOT) features in Release 7 (R7) use an RLC/MAC block containing more than the two (2) RLC data blocks.
EGPRS-2 UL Level A introduces five (5) new MCSs (UAS-7 to UAS-11) as shown in Table 3. An RLC/MAC block using UAS-10 and UAS-11 contains three (3) RLC data blocks. EGPRS-2 UL Level B introduces eight (8) new MCSs (UBS-5 to UBS-12) as shown in Table 4. An RLC/MAC block using UBS-9 and UBS-10 contains three (3) RLC data blocks, and an RLC/MAC data block using UBS-11 and UBS-12 contains four (4) RLC data blocks.
TABLE 3Channel CodingEGPRS RLC data unit size (N2)Scheme(octets)MCS-122MCS-228MCS-337MCS-444MCS-556MCS-674UAS-72 × 56UAS-82 × 64UAS-92 × 74UAS-103 × 56UAS-113 × 64
TABLE 4Channel CodingEGPRS RLC data unit size (N2)Scheme(octets)MCS-122MCS-228MCS-337MCS-444UBS-556UBS-674UBS-72 × 56UBS-82 × 74UBS-93 × 56UBS-103 × 74UBS-114 × 68UBS-124 × 74
EGPRS-2 UL (or, HUGE) has been carefully designed to operate in conjunction with the SSN-based FANR operation. While the SSN-based ACK/NACK mode may operate with EGPRs-2 UL (or HUGE) in the current state-of-the-art, the time-based ACK/NACK mode may currently not be employed in conjunction with EGPRS-2 transmission formats because of the prior art design assumption based on exclusive use only with EGPRS bursts. Therefore, no method has been provided for how a WTRU should deal with a configured time-based PAN field received in the DL when simultaneously using EGPRS-2 UL (or HUGE) transmissions in the UL. Similarly, no method has been provided for how a WTRU should deal with TB-FANR mode when using EGPRS-2 DL (or REDHOT) transmissions in the DL.